This invention relates to cleaving boules and more particularly to a process for cleaving single crystal materials such as silicon and germanium.
Typically, rods of single crystal material are cut into thin slices or wafers by a saw blade for further processing. These slices are usually on the order of 0.010 to 0.015 inch thick which is about the same thickness as the saw blades utilized. This type of operation for slicing or cleaving to achieve thin wafers results in losses of 50 percent or more of the expensive single crystal material.
U.S. Pat. No. 3,901,423 issued to Hillberry et al provides an improvement over the use of saw blades to slice these single crystal boules into thin wafers. The Hillberry patent provides a method whereby a crystal is fractured in a transverse manner to produce thin wafers. Hillberry et al imparts a desired stress distribution to the crystal which predetermines the direction of crack growth and then initiates the fracture at the desired location. Hillberry et al achieves fracturing by: (1) introducing a preselected stress concentration into the crystal; (2) applying an internal stress acting normally upon the desired fracture plane and (3) applying a sudden acting fracturing force at the desired point of fracture acting substantially perpendicular to the predetermined fracture plane.
The present invention is a process of cleaving a single crystal material (such as silicon or germanium) into thin wafers without the necessity of applying an internal stress which acts normal to the desired fracture plane. The present invention does not require that the fracture initiating force be applied directly at the point of the desired fracture. The process of the present invention does not tear or force the boule apart at a given point but rather applies pressure which allows the boule to cleave at its plane of minimum bond strength, thereby achieving a thin wafer having a smooth surface which does not require further extensive processing to prepare it for its ultimate use, for example, in semiconductors or solar devices.